This invention is directed to a process for preparing aldehydes from base sensitive amines. The process can be employed to obtain carboxylic acid methyl esters; in particular, thiazolidine carboxylic acid methyl ester which is useful as an intermediate in the preparation of bicyclic lactams. These bicyclic lactam compounds are potent angiotensin converting enzyme (ACE) inhibitors useful in the treatment of hypertension, congestive heart failure, and the like. (See, for example, U.S. Pat. Nos. 4,415,496; 4,661,479; and 4,371,444).
One prior art process discloses the preparation of an aldehyde which is then coupled with cysteine methyl ester to obtain a thiazolidine methyl ester [J. Biol. Chem, 198, 765 (1952); ibid, 192, 535 (1951)]. This process requires a long, cumbersome sequence involving enzymatic resolution of racemic material to obtain the desired thiazolidine intermediate. The final product is produced in low yields (.about.3%) which is not commerically or economically attractive.
In another prior art process, an aldehyde surrogate is produced which is then coupled with cysteine methyl ester from which the desired thiazolidine product is obtained in low yields (.about.10%-20%) only after prolonged and intensive chromatographic purification [JACS, 46, 1937 (1981)].